Roundabout 4 is expressed on hematopoietic stem cells and potentially involved in the niche-mediated regulation of the side population phenotype.
Roundabout (Robo) family proteins are immunoglobulin-type cell surface receptors that are expressed predominantly in the nervous system. The fourth member of this family, Robo4, is distinct from the other family members in that it is expressed specifically in endothelial cells. In this study, we examined the expression of Robo4 in hematopoietic stem cells (HSCs) and its possible role in HSC regulation. Robo4 mRNA was specifically expressed in murine HSCs and the immature progenitor cell fraction but not in lineage-positive cells or differentiated progenitors. Moreover, flow cytometry showed a correlation between higher expression of Robo4 and immature phenotypes of hematopoietic cells. Robo4(high) hematopoietic stem/progenitor cells presented higher clonogenic activity or long-term repopulating activity by colony assays or transplantation assays, respectively. A ligand for Robo4, Slit2, is specifically expressed in bone marrow stromal cells, and its expression was induced in osteoblasts in response to myelosuppressive stress. Interestingly, overexpression of Robo4 or Slit2 in HSCs resulted in their decreased residence in the c-Kit(+)Sca-1(+)Lineage(-)-side population fraction. These results indicate that Robo4 is expressed in HSCs, and Robo4/Slit2 signaling may play a role in HSC homeostasis in the bone marrow niche.
Shibata
Fumi
F
Advanced Clinical Research Center, University of Tokyo, Japan.
Goto-Koshino
Yuko
Y
Morikawa
Yoshihiro
Y
Komori
Tadasuke
T
Ito
Miyuki
M
Fukuchi
Yumi
Y
Houchins
Jeffrey P
JP
Tsang
Monica
M
Li
Dean Y
DY
Kitamura
Toshio
T
Nakajima
Hideaki
H
D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism; D002454:Cell Differentiation; D003114:Colony-Forming Units Assay; D005434:Flow Cytometry; D006412:Hematopoietic Stem Cells / Q000166:cytology / Q000378:metabolism*; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D051379:Mice; D039902:Multipotent Stem Cells / Q000166:cytology / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D010641:Phenotype; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic / Q000378:metabolism*; D015398:Signal Transduction; D055153:Stem Cell Niche / Q000378:metabolism*; D013312:Stress, Physiological; D017154:Stromal Cells / Q000166:cytology / Q000378:metabolism; D000098552:Slit Homolog 2 Protein
D036341:Intercellular Signaling Peptides and Proteins; D009419:Nerve Tissue Proteins; D011956:Receptors, Cell Surface; D011971:Receptors, Immunologic; C540792:Robo4 protein, mouse; D000098552:Slit Homolog 2 Protein